External Landmarks Research Articles

A population-based observational morphologic measurements of anatomic landmarks in maxillary and mandibular molar

Aim: The aim of this study is to study the morphological measurements of external and internal anatomic landmarks in human maxillary and mandibular molars and their correlation with critical pulp chamber morphology.Materials and Methods: A total of 200 mandibular and maxillary molar teeth of patients were evaluated. Teeth whose pulp chamber were not violated by caries, restoration, fracture crown, and those having closed apex were included in the study. Teeth were subjected to radiovisiography of bitewing projection and imaging tool was utilized for measuring-A: Distance from the pulp chamber floor to the furcation, B: Distance from the pulp chamber ceiling to the furcation, C: Distance from the buccal cusp tip to the furcation, D: Distance from the buccal cusp to the floor of the pulp chamber, E: Distance from the buccal cusp to the ceiling of pulp chamber, and F: Pulp chamber height. Differences in the measurements were examined using the Student's t-test and Pearson correlations. All results were considered statistically significant if P < 0.05.Results: There were significant differences found among the various measurements between young and old population groups (P < 0.05). The highest percentage variance was found for the height of the pulp chamber (P < 0.001).Conclusions: The knowledge of pulp chamber morphology should be integrated with preoperative radiograph and intraoperative tactile perception during endodontic access preparation.

A Systematic Approach to Dissection of the Equine Brain-Evaluation of a Species-Adapted Protocol for Beginners and Experts.

Introduction of new imaging modalities for the equine brain have refocused attention on the horse as a natural model for ethological, neuroanatomical, and neuroscientific investigations. As opposed to imaging studies, strategies for equine neurodissection still lack a structured approach, standardization and reproducibility. In contrast to other species, where adapted protocols for sampling have been published, no comparable guideline is currently available for equids. Hence, we developed a species-specific slice protocol for whole brain vs. hemispheric dissection and tested its applicability and practicability in the field, as well as its neuroanatomical accuracy and reproducibility. Dissection steps are concisely described and depicted by schematic illustrations, photographs and instructional videos. Care was taken to show the brain in relation to the raters' hands, cutting devices and bench surface. Guidance is based on a minimum of external anatomical landmarks followed by geometric instructions that led to procurement of 14 targeted slabs. The protocol was performed on 55 formalin-fixed brains by three groups of investigators with different neuroanatomical skills. Validation of brain dissection outcomes addressed the aptitude of slabs for neuroanatomical studies as opposed to simplified routine diagnostic purposes. Across all raters, as much as 95.2% of slabs were appropriate for neuroanatomical studies, and 100% of slabs qualified for a routine diagnostic setting. Neither autolysis nor subfixation significantly affected neuroanatomical accuracy score, while a significant negative effect was observed with brain extraction artifacts. Procedure times ranged from 14 to 66 min and reached a mean duration of 23.25 ± 7.93 min in the last of five trials in inexperienced raters vs. 16 ± 2.83 min in experts, while acceleration of the dissection did not negatively impact neuroanatomical accuracy. This protocol, derived analogously to the consensus report of the International Veterinary Epilepsy Task Force in dogs and cats, allows for systematic, quick and easy dissection of the equine brain, even for inexperienced investigators. Obtained slabs feature virtually all functional subcompartments at suitable planes for both diagnostic and neuroscientific investigations and complement the data obtained from imaging studies. The instructive protocol and brain dissection videos are available in Supplementary Material.

Computed Tomography-Derived Occipital-Coccygeal Length and Ilium Wing Distance Correlates with Skin to Epidural and Intrathecal Depths in Dogs.

The current clinical techniques for neuraxial needle placement in dogs are predominantly blind without prior knowledge of the depth required to reach the desired space. This study investigated the correlation and defined the relationship between easily obtainable external landmark variables in the dog; occipital–coccygeal length (OCL) and ilium wings distance (IWD), with the skin to epidural and intrathecal space distances using computed tomography (CT). The CT images of 86 dogs of different breeds were examined in this retrospective observational study. Images of dogs in sternal recumbency were optimized to the sagittal view. The distances between the skin and lumbosacral epidural space (LSE) and skin to sacrococcygeal space (SCE) were measured to the ligamentum flavum surrogate (LFS) line. The distance between the skin and the intrathecal space (ITS) was measured from the skin to the vertebral canal at the interlumbar (L5–L6) space. Measurements of the IWD and OCL were performed on dorsal and scout views, respectively. Linear regression equations and Pearson’s correlation coefficients were calculated between variables. Data were reported as mean (standard deviation). Significance was set as alpha < 0.05. After exclusion of four dogs, 82 CT scans were included. The depths were LSE 45 (15) mm, SCE 23 (10) mm, and ITS 50 (15) mm. There was a moderate correlation between OCL with LSE (=14.2 + OCL * 0.05 (r = 0.59, p < 0.0001)), and a strong correlation with ITS (=11.4 + OCL * 0.07 (r = 0.76, p < 0.0001)), while a very weak correlation was found with SCE (=14.0 + OCL * 0.02 (r = 0.27, p < 0.0584)). Similarly, with IWD, there was a moderate correlation with LSE (=10.8 + IWD * 0.56 (r = 0.61, p < 0.0001)), and strong correlation with ITS (=9.2 + IWD * 0.67 (r = 0.75, p < 0.0001)), while a weak correlation was found with SCE (=11.2 + IWD * 0.2 (r = 0.32, p < 0.0033)). Mathematical formulae derived from the multiple regression showed that the body condition score (BCS) improved the relationship between IWD and OCL and the LSE, SCE and ITS, while the addition of body weight was associated with multicollinearity. Further studies are required to determine the accuracy of the algorithms to demonstrate their ability for prediction in a clinical setting.

Neuroanatomy and Sampling of Central Projections for the Visual System in Mammals Used in Toxicity Testing.

Visual system toxicity may manifest anywhere in the visual system, from the eye proper to the visual brain. Therefore, effective screening for visual system toxicity must evaluate not only ocular structures (ie, eye and optic nerve) but also multiple key brain regions involved in vision (eg, optic tract, subcortical relay nuclei, and primary and secondary visual cortices). Despite a generally comparable pattern across species, the neuroanatomic organization and function of the visual brain in rodents and rabbits exhibit appreciable differences relative to nonrodents. Currently recognized sampling practices for general toxicity studies in animals, which are based on easily discerned external neuroanatomic landmarks and guided by extant stereotaxic brain atlases, typically will permit histopathologic evaluation of many brain centers involved in visual sensation (eg, optic chiasm, optic tract, dorsal lateral geniculate nucleus, primary and secondary visual cortices) and often some subcortical brain nuclei involved in light-modulated nonvisual activities needed for visual attention and orientation (eg, rostral colliculus in quadrupeds, termed the superior colliculus in bipeds; several cranial nerve nuclei). Pathologic findings induced by toxicants in the visual brain centers are similar to those that are produced in other brain regions.

Successfully REBOA performance: does medical specialty matter? International data from the ABOTrauma Registry

BackgroundResuscitative endovascular balloon occlusion of the aorta (REBOA) is a minimally invasive procedure being increasingly utilized to prevent patients with non-compressible torso hemorrhage from exsanguination. The increased use of REBOA is giving rise to discussion about “Who is and who should be performing it?”MethodsData from the international ABO (aortic balloon occlusion) Trauma Registry from between November 2014 and April 2020 were analyzed concerning the question: By who, how, and where is REBOA being performed? The registry collects retrospective and prospective data concerning use of REBOA in trauma patients.ResultsDuring the study period, 259 patients had been recorded in the registry, 72.5% (n = 188) were males with a median (range) age of 46 (10-96) years. REBOA was performed in the ER in 50.5%, in the OR in 41.5%, and in the angiography suite in 8% of patients. In 54% of the patients REBOA was performed by surgeons (trauma surgeons 28%, vascular surgeons 22%, general surgeons 4%) and in 46% of the patients by non-surgeons (emergency physicians 31%, radiologists 9.5%, anesthetists 5.5%). Common femoral artery (CFA) access was achieved by use of external anatomic landmarks and palpation alone in 119 patients (51%), by cutdown in 57 patients (24%), using ultrasound in 49 patients (21%), and by fluoroscopy in 9 patients (4%). Significant differences between surgeons and non-surgeons were found regarding patient’s age, injury severity, access methods, place where REBOA was performed, location patients were taken to from the emergency room, and mortality.ConclusionA substantial number of both surgical and non-surgical medical disciplines are successfully performing REBOA to an almost equal extent. Surgical cutdown is used less frequently as access to the CFA compared with reports in older literature and puncture by use of external anatomic landmarks and palpation alone is used with a high rate of success. Instead of discussing “Who should be performing REBOA?” future research should focus on “Which patient benefits most from REBOA?”

Landmark-Centered Coding in Frontal Cortex Visual Responses

Visual landmarks influence spatial cognition, navigation and goal-directed behavior, but their influence on visual coding in sensorimotor systems is poorly understood. We hypothesized that visual responses in frontal cortex gaze control areas encode potential targets in an intermediate gaze-centered / landmark-centered reference frame that might depend on specific target-landmark configurations rather than a global mechanism. We tested this hypothesis by recording neural activity in the frontal eye fields (FEF) and supplementary eye fields (SEF) while head-unrestrained macaques engaged in a memory-delay gaze task. Visual response fields (the area of visual space where targets modulate activity) were tested for each neuron in the presence of a background landmark placed at one of four oblique configurations relative to the target stimulus. 102 of 312 FEF and 43 of 256 SEF neurons showed spatially tuned response fields in this task. We then fit these data against a mathematical continuum between a gaze-centered model and a landmark-centered model. When we pooled data across the entire dataset for each neuron, our response field fits did not deviate significantly from the gaze-centered model. However, when we fit response fields separately for each target-landmark configuration, the best fits shifted (mean 37% / 40%) toward landmark-centered coding in FEF / SEF respectively. This confirmed an intermediate gaze / landmark-centered mechanism dependent on local (configuration-dependent) interactions. Overall, these data show that external landmarks influence prefrontal visual responses, likely helping to stabilize gaze goals in the presence of variable eye and head orientations.

Anatomic Study Quantifying the Relationship Between the Arcuate Eminence and the Root of the Zygoma: Application to Skull Base Surgery

The aim of this study was to define the structural relationship between the arcuate eminence (AE) and a known fixed external bony landmark, the root of the zygoma (ZR), and to determine its reliability as a consistent guide for guiding surgical approaches. To our knowledge, this is the only anatomic study to quantify the relationship between the AE and ZR. Twenty-one dry temporal bones were measured using digital calipers. The distance from the posterior aspect of the ZR to the midpoint of the AE was measured. Additionally, the anteroposterior distance between the ZR and AE and vertical distance between the 2 structures were measured. Student's t-test was used to compare the left and right sides. An AE was found in every specimen. The mean ZR to AE distance was 30.9 mm. On most sides (91%), the ZR was located more inferiorly than the AE with a mean distance of 3 mm between the 2 structures. The mean distance between the AE and ZR was 17 mm. On all sides, the AE was located posterior to the ZR. No significant differences were found between sides. No anatomic variations or pathologic conditions were noted in any of the specimens. The ZR is an easily identifiable and consistent bony landmark often used by skull base surgeons. In this investigation, we measured the anatomic relationships between the ZR and AE. Such data might assist in planning surgical trajectories and minimizing complications when skull base pathologies are approached.

New diagnostic approach of the different types of isolated craniosynostosis

In this study, we diagnose skull shape deformities by analysing sinusoid curves obtained from standardized computed tomography (CT) slices of the skull for the common craniosynostoses (scaphocephaly, brachycephaly, trigonocephaly, right- and left-sided anterior plagiocephaly). Scaphocephaly has a high forehead peak and low troughs, in contrast to brachycephaly. Anterior plagiocephaly has asymmetry and shifting of the forehead peak. Trigonocephaly has a high and narrow frontal peak. Control patients have a symmetrical skull shape with low troughs and a high and broader frontal peak. Firstly, we included 5 children of every group of the common craniosynostoses and additionally 5 controls for extraction and calculation of characteristics. A diagnostic flowchart was developed. Secondly, we included a total of 51 craniosynostosis patients to validate the flowchart. All patients were correctly classified using the flowchart.Conclusion: Our study proposes and implements a new diagnostic approach of craniosynostosis. We describe a diagnostic flowchart based on specific characteristics for every type of craniosynostosis related to the specific skull deformities and control patients. All variables are expressed in number; therefore, we are able to use these variables in future research to quantify the different types of craniosynostosis.What is Known:• Premature fusion of one or more cranial sutures results in a specific cranial shape.• Clinical diagnosis is relatively simple; however, objective diagnosis based on distinctive values is difficult.What is New:• Using external landmarks and curve analysis, distinctive variables, and values for every type of craniosynostosis related to the specific skull deformities were determined and used to create a diagnostic flowchart for diagnosis.• Validation with an independent data set of 51 patients showed that all patients were correctly classified.

Anatomy and external landmarks of the superficial temporal artery using 3-dimensional computed tomography.

The purpose of this study was to analyze the anatomical variability of the superficial temporal artery (STA) and to provide an easy visual landmark to find the STA and its branches to facilitate its surgical access. A retrospective study was conducted on 57 patients who underwent a head and neck computed tomography with contrast injection. A visual landmark running from the tragus to the corner of the eye was used: the "eye-tragus-line" (ETL). On the ETL, the distance between the tragus and the STA was measured. The length of the STA main branch, its parietal and frontal branch and the angle of the STA and its branches with the ETL were measured. The division of the STA was studied as above/at the same level/below the zygomatic arch (ZA) and the ETL. The STA division was located above the ZA in 61.54% of cases, at the same level in 26.92% of cases and below in 11.54% of cases. Regarding the ETL, 93.27% of the STA divisions were located above the ETL, 5.77% at the same level and 0.96% below. On the ETL, the STA was located 15.55 ± 4.5mm in front of the tragus. This study allowed to define an easy visual landmark: the ETL running from the tragus to the corner of the eye. The STA main branch was located 15.55 ± 4.5mm of front of the tragus on the ETL. The STA division was nearly always located above the ETL (99.04%). Furthermore, this study provides a statistical representation of the anatomy of the STA and its branches.

Exploring Spatial Cognitive Process Among STEM Students and Its Role in STEM Education

Spatial ability is a powerful systematic source of individual differences in the areas of science, technology, engineering, and technology (STEM). Abundant research has evidenced that psychometrically assessed spatial ability is a strong predictor of STEM achievement. However, its underlying cognitive process and relevant role in STEM education are unknown. From the perspective of cognitive neuroscience, spatial ability is also considered a human intelligence deriving from the cognitive processing of spatial information in the brain. With the help of the cognitive neuroscience paradigm of spatial navigation, in the present work, we investigate the spatial cognitive process among STEM students and its role in STEM education. A total of 172 undergraduates majoring in veterinary science participated in a spatial navigation test. Participants attempted to return a toy to its original place in an arena when given either internal self-motion cues only, external landmark cues only, or both in a spatial navigation task. Modelling analysis of 172 participants’ spatial navigation behaviours showed that all the participants’ spatial cognitive processes featured navigation cue integration. The results of the different tests showed that students with higher levels of navigation cue integration had better academic performance in STEM learning. The results also indicated that, surprisingly, better academic performance in science and mathematics relied more on the use of internal self-motion cues, while better academic performance in engineering and technology relied more on the use of external landmark cues. This study sheds some light on the spatial cognitive process and its role in STEM education from the cognitive neuroscience perspective, thus deepening the functional understanding of spatial ability as a systemic source of individual differences for STEM education, and provides an empirical reference point for interdisciplinary studies on the role of cognition in the context of STEM education. Implications on STEM learning design and STEM teaching were discussed.

Quantification of Severity of Unilateral Coronal Synostosis.

Objectives:Severity of unilateral coronal synostosis (UCS) can vary. Quantification is important for treatment, expectations of treatment and natural outcome, and education of the patient and parents.Design:Retrospective study.Setting:Primary craniofacial center.Patients, Participants:Twenty-three preoperative patients with unilateral coronal craniosynostosis (age < 2 years).Intervention:Utrecht Cranial Shape Quantifier (UCSQ) was used to quantify severity using the variables: asymmetry ratio of frontal peak and ratio of frontal peak gradient.Main Outcome Measures(s):The UCSQ variables were combined and related to visual score using Pearson correlation coefficient; UCSQ and visual score were additionally compared to Di Rocco classification by one-way analysis of variance or Kruskal-Wallis test. All measurements were made on computed tomography scans.Results:Good correlation between UCSQ and visual score was found (r = 0.67). No statistically significant differences were found between group means of UCSQ in the 3 categories of Di Rocco classification (F 2,20 = 0.047; P > .05). Kruskal-Wallis test showed no significant differences between group means of visual score in the 3 categories of Di Rocco classification (Kruskal-Wallis H (2) = 0.871; P > .05).Conclusions:Using UCSQ, we can quantify UCS according to severity using characteristics, it outperforms traditional methods and captures the whole skull shape. In future research, we can apply UCSQ to 3D-photogrammetry due to the utilization of external landmarks.

The Longissimus Capitis Insertion as a Superficial Landmark for the Sigmoid Sinus: An Anatomical Study.

Objective Many external anatomical landmarks have been used for approximating deeper, intracranial structures. Herein, we evaluate the attachment of the longissimus capitis (LC) on the mastoid process as a landmark for the underlying sigmoid sinus. Methods Adult cadavers underwent dissection of the posterior occiput with special attention to the attachment of the LC muscle. Once the periphery of the muscle's tendon of attachment was determined, a burr hole was made in this area and evaluated internally for its relationship to the sigmoid sinus. Results From an intracranial view, burr holes on all sides were over the sigmoid sinus and just slightly lateral to the center of the sinus. The distance from the midline to the medial border of the insertion of the LC had a mean of 63.0 ± 7.2 mm. The width of the tendon of insertion of the LC on the mastoid process had a mean of 17.6 ± 5.7 mm. The length of the tendon insertion of the LC had a mean of 14.7 ± 4.7 mm. The distance from the inferior border of the insertion of the LC to the tip of the mastoid process had a mean of 6.2 ± 4.5 mm. Conclusion To our knowledge, use of the attachment site of the LC on the mastoid process as an external landmark for the underlying sigmoid sinus has not previously been reported. Based on our cadaveric findings, the sigmoid sinus is centered under the attachment of the LC regardless of the width of its tendon.

Establishing a New Bony Landmark for Safe Screw Insertion in Medial Displacement Calcaneal Osteotomy: A Simulation-Based Approach

Category:Hindfoot; OtherIntroduction/Purpose:Medial displacement calcaneal osteotomy (MDCO) is a commonly performed procedure in flatfoot reconstruction. Fixation is often achieved with screws due to its ability to compress across the osteotomy site. Screws are placed via a free-handed technique without direct fluoroscopic visualization, due to difficulty attaining a simultaneous axial calcaneal view. In addition, the posterior calcaneal tuber translates medially after displacement, resulting in altered anatomical geometry. It is therefore important to establish a reliable external bony landmark when performing free-handed interfragmentary fixation in order to avoid potential screw-related complications and to provide better surgical technique and fixation. The purposes of this study are to validate a new external bony landmark and to establish the appropriate trajectory and screw length for free-hand screw fixation in MDCO.Methods:A total of 84 postoperative computed tomography (CT) scans of MDCO in 70 patients were analyzed. The images were reconstructed using a 3-dimensional simulation program (Vworks 4.0, Cybermed). Virtual screw insertion was simulated by aiming towards two bony landmarks: the base of the 5th metatarsal in the axial plane, and the sinus tarsi in the sagittal plane (Figure 1). A grading system was also utilized to classify scenarios in which the screw breached the distal cortical wall: Grade 1 was defined as contact between the virtual screw and the cortex, Grade 2 as the screw approaching the outer margin of the cortex, and Grade 3 as the screw penetrating the outer cortex. The trajectory angle between the screw and the osteotomy, as well as the screw size, were also measured.Results:The average age of patients was 24.5 (range, 19 to 53), and 100% were males. The average displacement of the posterior calcaneal fragment was 7.3+-1.5 mm (range, 3.9 to 13.8). Among the 84 virtual screws, only five (6.0%) breached the medial cortical wall of the osteotomized calcaneus. All medial breaches were Grade 1. None of the virtual screws breached the lateral cortical wall. Mean trajectory angle between the virtual screw and the osteotomy site was 74.9+-6.7˚ (range, 60.0 to 89.8˚). In the perioperative data, estimated maximum screw length by simulation was 55.6+-4.4 mm (range, 50 to 65).Conclusion:Our results suggest that the optimal trajectory of free-handed screw placement can be determined through simulation of calcaneal interfragmentary screw insertion using postoperative CT imaging. Using this simulation technology, we determined a trajectory towards the sinus tarsi on the sagittal plane and the base of the 5th metatarsal on the axial plane to be a reliable external bony landmark for placement of screws in MDCO. These promising results have potential implications in achieving better fixation as well as improving union rates and operative outcomes.

Relationship of superior sagittal sinus with sagittal midline: A surgical application.

Background: Interhemispheric approach is widely used to surgical management of midline tumors and vascular lesion in and around the third ventricle. Complete exposure of the superior sagittal sinus to obtain adequate working space of midline lesion is difficult, because of the risk to inadvertent injury to the sinus and bridging veins, which may cause several neurological deficits. Understanding the SSS neuroanatomy and its relationships with external surgical landmarks avoid such complications. The objective of this study is to accurately describe the position of SSS and its displacement in relation with sagittal midline by magnetic resonance imaging.Methods: A retrospective cross-sectional, observational study was performed. Magnetic resonance image of 76 adult patients with no pathological imaging was analyzed. The position of the halfway between nasion and bregma, bregma, halfway between bregma and lambda, and lambda was performed. The width and the displacement of the superior sagittal sinus accordingly to the sagittal midline were assessed in those landmarks.Results: The mean width of superior sagittal sinus at halfway between nasion and bregma, bregma, halfway between bregma and lambda, and lambda was 5.62 ± 2.5, 6.5 ± 2.8, 7.4 ± 3.2, and 8.5 ± 2.1 mm, respectively, without gender discrepancy. The mean displacement according to the midline at those landmarks showed a statistically significant difference to the right side among sexes.Conclusion: In this study, we demonstrate that sagittal midline may approximate external location of the superior sagittal sinus. Our data showed that in the majority of the cases, the superior sagittal sinus is displaced to the right side of sagittal midline as far as 16.3 mm. The data we obtained provide useful information that suggest that neurosurgeons should use safety margin to perform burr holes and drillings at the sagittal midline.

Nasal Sidewall Dimensions in the Asian Nose: A Thai Cadaveric Study.

Nasal bone length remains a commonly referenced attribute when referring to the aesthetic nose. Short nasal bone length is suggested to predispose to a greater risk of middle vault collapse after rhinoplasty. We report on normative measurements of nasal bones and associated structures in Thai cadavers. Using twelve adult cadavers, common external nasal landmarks were identified and measured to approximate the dimensions of the nasal bones and upper lateral cartilages. These clinically relevant surface landmarks were correlated to direct measurements of dissected nasal bones and the upper lateral cartilage in these same cadavers. Additionally, external landmarks of ten volunteers were examined. The average measured length of the nasal bone was 19.00mm; the average measured length of the upper lateral cartilage was 13.15mm. Measurements obtained via external landmarks were 17.60mm and 13.05mm respectively. The relationship of the nasal bone internal length to the external measurement (A) was a ratio of 1.10:1, whereas the internal length of the upper lateral cartilage to the corresponding external measurement (B) was 1.04:1. On average the nasal bones contributed to 59% of the middle vault nasal sidewall. The average length of the Thai adult nasal bone is 19.00mm while that of the upper lateral cartilage is 13.15mm. The relationships of the accepted external landmarks to the underlying anatomic structures were established using a t test. This normative data will generate useful parameters when evaluating the Asian rhinoplasty patient.

A calcaneal tunnel for CFL reconstruction should be directed to the posterior inferior medial edge of the calcaneal tuberosity.

Anatomical reconstruction of the calcaneofibular ligament (CFL) is a common technique to treat chronic lateral ankle instability. A bone tunnel is used to fix the graft in the calcaneus. The purpose of this study is to provide some recommendations about tunnel entrance and tunnel direction based on anatomical landmarks. The study consisted of two parts. The first part assessed the lateral tunnel entrance for location and safety. The second part addressed the tunnel direction and safety upon exiting the calcaneum on the medial side. In the first part, 29 specimens were used to locate the anatomical insertion of the CFL based on the intersection of two lines related to the fibular axis and specific landmarks on the lateral malleolus. In the second part, 22 specimens were dissected to determine the position of the neurovascular structures at risk during tunnel drilling. Therefore, a method based on four imaginary squares using external anatomical landmarks was developed. For the tunnel entrance on the lateral side, the mean distance to the centre of the CFL footprint was 2.8 ± 3.0mm (0-10.4mm). The mean distance between both observers was 4.2 ± 3.2mm (0-10.3mm). The mean distance to the sural nerve was 1.4 ± 2mm (0-5.8mm). The mean distance to the peroneal tendons was 7.3 ± 3.1mm (1.2-12.4mm). For the tunnel exit on the medial side, the two anterior squares always contained the neurovascular bundle. A safe zone without important neurovascular structures was found and corresponded to the two posterior squares. Lateral landmarks enabled to locate the CFL footprint. Precautions should be taken to protect the nearby sural nerve. A safe zone on the medial side could be determined to guide safe tunnel direction. A calcaneal tunnel should be directed to the posterior inferior medial edge of the calcaneal tuberosity.

Montgomery's Aperture: An External Anatomic Landmark for Surgical Identification of the Anterior Commissure

This study evaluates the consistency of palpable identification of an external landmark for the anterior commissure (AC), termed Montgomery's aperture (MA), in cadaveric and surgical settings. Part 1: In human cadaveric larynges, palpation of the external laryngeal framework was used to identify MA by three blinded otolaryngologists. The vertical height (VH) of the thyroid cartilage and distance from MA to the inferior border of the thyroid cartilage were measured, larynges were bisected, and the AC was identified and measured. Surface anatomy was demonstrated visually using 3D imaging. Part 2: Retrospectively collected case series used palpation of MA in thyroplasty type 1 (TT1) and compared the result to ½ VH. Part 1: MA was identified in seven cadavers by three surgeons. In four of seven MA was palpated at the location of AC. The average difference between the AC and MA was -0.95 ± 0.96 mm. The average difference between AC and ½VH was 0.08 ± 0.72 mm. Part 2: In 49 patients (57% females) who underwent TT1, MA correlated within ½VH in 67% of cases. MA was inferior to ½VH in 27% of cases, on average 1.08 mm ± 0.51 mm below ½VH. MA was not palpable in 6% (3 of 49) of patients. We define the MA as the external indentation or flattening of the thyroid cartilage located within 1 millimeter inferior or at ½ VH of the thyroid cartilage. MA is a reliable, reproducible, palpable landmark for the anterior commissure. It serves as an important landmark that can be used in laryngoplastic surgery in which accurate prediction of the glottis is important.

Immersive Surgical Anatomy of the Craniometric Points.

Craniometric points (CPs) have been used in neurosciences since the 1800s. Localization of the CPs allows for the identification of crucial intracranial structures. Despite the contribution of advanced technology to surgery, the knowledge of these points remains crucial for surgical planning and intraoperative orientation. The understanding of these crucial points can be facilitated with the use of three-dimensional technology combined with anatomical dissections. The present study is part of a stereoscopic collection of volumetric models (VMs) obtained from cadaveric dissections that depict the relevant anatomy of the CPs. Five embalmed heads and two dry skulls have been used to depict these points. After the anatomical dissection, stereoscopic images and VMs were generated to show the correlation between external and internal landmarks. The CPs identified were divided into sutures, suture junctions, prominences and depressions, and cortical surface landmarks. The VMs represent an interactive way to define these points easily and their correlation with different intracranial structures (vascular structure, ventricle cavity, and Brodmann’s areas).

Lateral Limit of Superior Sagittal Sinus in Respect to External Part of Sagittal Suture

Background: Sagittal suture has been used as an external landmark of superior sagittal sinus since the very beginning of neurosurgery. However, most of the time the sinus is not exactly under the suture line, rather, it has some displacement to one side. So, to analyze the variation of the lateral limit of superior sagittal sinus from the external part of sagittal sinus this study was performed.&#x0D; Materials and methods: Consecutive cases of MRI brain with contrast done in B&amp;C Medical College Teaching Hospital was collected over 3 months, Age, gender, right, and left lateral limits of the superior sagittal sinus from the sagittal suture at its mid-point was collected in preformed proforma. Mean and standard deviation was calculated for the continuous variables, ANOVA was done to evaluate the association of gender with the lateral limits of sinus and Pearson correlation was done to see the relation of age with the lateral limits of the sinus. All the analysis was done using IBM SPSS 20.&#x0D; Results: There were a total of 40 patients enrolled in the study. The mean age was 39.8 years with male (75%) predominance. The lateral right limit of the superior sagittal sinus was up to 23mm and in the left up to 17.1mm from the outer limit of the sagittal suture. There was no significant association of gender with both the right and left limits of the superior sagittal sinus. Similarly, there was no significant correlation of age with the lateral limit of the superior sagittal sinus.&#x0D; Conclusion: The mean existence of superior sagittal sinus is 9.57mm in the right to 5.78mm in the left side from the outer limit of the sagittal suture. However, in extreme stances it's lateral limits can extend up to 17mm in left to 23mm in the right from the outer limit of the sagittal suture.

A Thalamic Reticular Circuit for Head Direction Cell Tuning and Spatial Navigation

As we navigate in space, external landmarks and internal information guide our movement. Circuit and synaptic mechanisms that integrate these cues with head-direction (HD) signals remain, however, unclear. We identify an excitatory synaptic projection from the presubiculum (PreS) and the multisensory-associative retrosplenial cortex (RSC) to the anterodorsal thalamic reticular nucleus (TRN), so far classically implied in gating sensory information flow. Invitro, projections to TRN involve AMPA/NMDA-type glutamate receptors that initiate TRN cell burst discharge and feedforward inhibition of anterior thalamic nuclei. Invivo, chemogenetic anterodorsal TRN inhibition modulates PreS/RSC-induced anterior thalamic firing dynamics, broadens the tuning of thalamic HD cells, and leads to preferential use of allo- over egocentric search strategies in the Morris water maze. TRN-dependent thalamic inhibition is thus an integral part of limbic navigational circuits wherein it coordinates external sensory and internal HD signals to regulate the choice of search strategies during spatial navigation.